The solvated sample component separation capability of Capillary Zone Electrophoresis, (CZE), systems is well known. As well, the ability of Direct Injection Nebulizer, (DIN), systems to nebulize small volume samples into a multiplicity of small diameter droplets for entry into, for instance, a closely situated Inductively Coupled Plasma system to ionize said sample components, is well known. Further, the sample analysis capabilities of Inductively Couple Plasma-Mass Spectrometer (ICP-MS), systems are well established. What has to date not been known, however, is a system for interfacing (CZE) systems with (ICP-MS) systems, utilizing a modified (DIN) system which comprises a sample introduction electrophoresis capillary tube. It should be apparent that such a system for interfacing would provide valuable utility.
Briefly, a (CZE) system comprises a capillary tube, one end of which is placed in a source of sample component containing solution, and another end of which is positioned distally. In use a voltage is applied between the ends of said capillary tube such that sample component containing solution is caused to migrate therethrough. Depending on the mass and charge of a sample component therein, and such factors as the PH of the solution forming solvent, different sample components travel through said capillary tube at different velocities, thereby arriving at the distal end thereof in a separated manner.
An (ICP-MS) system comprises an Inductively Coupled Plasma system followed by a Mass Spectrometer. An (ICP) system typically comprises an (ICP) "Torch" with an enclosed space therein in which a plasma is inductively formed by application of high frequency electrical energy, via a coil situated around said enclosed space. An (ICP) Torch, it is mentioned, comprises a "Sample Injector Tube" present concentrically and centrally within various other concentrically surrounding tubes, which various other concentrically surrounding tubes typically project beyond the projecting end of said sample injector tube, thereby providing an enclosed space therewithin, beyond the projecting end of said sample injector tube. Typically, during use, a sample solution is distally nebulized, (ie. atomized into small diameter droplets), and the nebulized droplets are caused to flow through said sample delivery tube into said plasma containing enclosed space. Gas is simultaneously caused to flow through annular spaces between concentric tubes within said (ICP) Torch with the effect being that nebulized sample is directed into the plasma containing enclosed space in a plume. When a sample component is injected into said plasma containing enclosed space of an (ICP) Torch, electrons therein are excited into high energy atomic orbitals and some are even dislodged therefrom, thereby providing ionized sample components. A (MS) system comprises means for identifying ionized, charged, sample components based upon their mass and charge by detecting said ionized charged sample component trajectory in the presence of electric and magnetic fields.
A (DIN) is a system for nebulizing small volumes of sample component containing solution. DIN's comprise a sample delivery tube concentrically centrally present within an essentially elongated tubular space through a "primary body element", such that during use sample component containing solution can be caused to eject from an end of said sample delivery tube simultaneous with the ejecting of a concentric gas from an annular space formed between the outer surface of said sample delivery tube, and the inner surface of the elongated tubular space through said primary body element. Interaction between said ejecting sample component containing solution and said gas causes said sample component containing solution to become nebulized into small droplets.
A Search of relevant references has identified an article titled "Zone Electrophoresis in Open-Tubular Glass Capillaries", by Jorgenson and Lukacs, Anal. Chem. 1981, Vol. 53, 1298-1302. This article describes a system for performing (CZE) in open-tubular glass capillaries with seventy-five (75) micron inner diameter with voltages up to thirty kilovolts (30 KV) applied thereacross to allow electroosmotic flow of positive and negative ions of a variety of sizes such that analysis thereof can occur in a single run.
A Patent to Fassel et al., No. 4,575,609 describes a micro nebulizer which inserts in, and mounts directly to a sample injector tube of a standard (ICP) torch. U.S. Pat. Nos. 5,212,365 and 5,272,308 to Wiederin describe improved (DIN) systems which do not require the presence of an (ICP) Torch sample injector tube as a part of their construction, but rather provide an elongated primary body element with a longitudinally oriented hole therethrough, through which longitudinally oriented hole a centrally located sample delivery tube extends. The Wiederin (DIN) systems allows for easy access to the space inside the Primary Body Element to allow nondestructive cleaning, and allows easy adjustment of the location of the relative positions of the sample ejecting end of the Sample Delivery Tube and the end of the Primary Body Element. Said adjustment allows optimizing the nebulizing ability of the Wiederin (DIN). A Meyer, U.S. Pat. No. 4,990,740 describes a low operational pressure (DIN)-like system at a lower aspect thereof, with a series of impactors thereabove. Said impactors serve to deflect large diameter droplets, (over approximately fifteen (15) microns in diameter), away from injection into an upper aspect of said system.
A Chan et al. U.S. Pat. No. 5,233,156 teaches Torches of the type used in (ICP) systems, which Torches are designed for use with high solids content samples. Standard (ICP) torches are also described therein.
A Smith et al., U.S. Pat. No. 4,885,076 describes a system in which a sample solution is subjected to an electrophoresis process to separate sample components, and in which an electrospray process serves to simultaneously nebulize and ionize the resulting sample solution. Use of a sheath liquid to make electrical contact to a sample solution discharge is mentioned. Another Patent in the same general area is U.S. Pat. No. 4,994,165 to Lee et al. This Patent focuses on a system for providing "make-up" fluid in a "liquid junction system", generally functionally similar to the Smith et al. system, which make-up fluid replaces fluid lost during the electrospray process. A Patent to Hall et al. describes an electrospray system in which a concentric flow of gas serves to focus the nebulized ionized droplets of an electrospray process.
A very recent article, by Olesik, Kinzer and Olesik titled "Capillary Electrophoresis Inductively Coupled Plasma Sepctrometry for Rapid Elemental Speciation", Anal. Chem. Vol. 67, No. 1, January 1995, describes a combined Capillary zone electrophoresis and pneumatic nebulizer system for use in providing an aerosol for introduction into inductively coupled plasma and mass spectrometer sample analysis systems. The described system provides that a capillary tube be connected within a pneumatic nebulizer system by way of silver paint, said silver paint serving to provide a snug fit thereof within said pneumatic nebulizer, and to provide an electrical contact to the end of the capillary tube thereby allowing electrophoresis effecting voltage to be applied thereto. While the system described is sufficient for investigative purposes, use in a commercial setting would be difficult. In addition, untoward contamination of sample analyte containing capillary effluent with silver, from the silver paint present at the end of the capillary tube can occur.
A need exists for a convenient to use system which provides means for a sample component containing solution to be subjected to a (CZE) process to provide separated sample components, followed by nebulization by a modified (DIN) system comprising a sample introduction electrophoresis capillary tube. Said system, during use, providing a multiplicity of nebulized small diameter sample component containing droplets, followed by injection into a (ICP) system wherein ionization of sample components occurs, which typically is followed by entry to a (MS) system for detection and analysis of the sample component content therein.
The present invention provides the missing teachings.